GB2574914A

GB2574914A - Method and apparatus for preparing animal feed

Info

Publication number: GB2574914A
Application number: GB201900473A
Authority: GB
Inventors: Mitchell Aidan
Original assignee: John Thompson and Sons Ltd
Current assignee: John Thompson and Sons Ltd
Priority date: 2018-06-21
Filing date: 2019-01-14
Publication date: 2019-12-25
Anticipated expiration: 2039-01-14
Also published as: GB201810179D0; GB2574864A; GB201900473D0; GB2574914B; IE20190094A2; IE87442B1

Abstract

Preparing animal feed includes splitting an incoming ingredient batch into at least two portions and feeding each portion to respective grinders 6, 8 arranged in parallel. The time taken for the grinders to grind their respective portions is determined, and the relative sizes of portions in subsequent batches is adjusted based on the difference in time each grinder took to grind its portion of a previous batch so as to minimise differences in grinding times for the portions in subsequent batches. A first portion may be fed to a first grinder, and a second portion subsequently fed to a second grinder. Batches may be portioned by a mechanical device 4, e.g. a moveable wall or diverter plate in a flow passage, or a screw conveyor with selectively openable outlets leading to the respective grinders (see figure 2). The portions may be recombined downstream of the grinders prior to a mixing step 10. The method may additionally comprise blending, wetting, conditioning 14, pelleting 16, cooling 18, and oil coating steps. An apparatus is also claimed, comprising parallel grinders 6,8, batch portioning means 4, and control means (not shown) for determining subsequent batch portioning sizes based on prior batch process times.

Description

Method and Apparatus for Preparing Animal Feed

FIELD OF THE INVENTION

This invention relates to a method and apparatus for preparing animal feed and in particular to a method and apparatus for preparing animal feed including a grinding step for grinding one or more ingredients.

BACKGROUND OF THE INVENTION

Animal feed is typically prepared in a compounding mill, wherein weighed batches of ingredients are ground, mixed and blended together with binders and other additives before being pressed into pellets or meal for supply to farmers. The first three stages; weighing, grinding and mixing, are collectively described within the industry as a blending operation.

An important step in the blending operation is the grinding of feed materials, primarily vegetable matter such as grains, pollard, soya, sunflower, distillers grains and palm kernel, to pre-determined particle size in one or more grinders to ensure the homogeneity of the finished product and to produce the physical attributes required.

In order to increase the capacity of the mill it is known to provide two or more grinders arranged in parallel such that multiple batches of ground material can be produced simultaneously. The incoming feed batch of material may be split into separate portions or sub-batches to be fed to each grinder, or subsequent batches may be consecutively fed to each grinder in turn, and then recombined into the next process, for example upstream of a mixer.

The efficiency of each grinder or set of grinders may vary over time due to wear.

Grinding times through each grinder will vary over several days or weeks as various components of each grinder pass through their natural wear/maintenance periods and due to the air density changes effecting the air flow and suction of material through screens and the clogging of filters and dust bags which also effects the air flow and hence grinder throughput. The overall length of time for the grinding process will be limited by the slowest grinder or grinder set. Therefore there is a desire to optimise the relative sizes of the portions of the incoming batch of material supplied to each hopper so that the grinding time for each batch is substantially the same. An object of the present invention is to overcome this problem and to minimise the length of time of the grinding step.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method for preparing animal feed including a grinding step for grinding one or more ingredients, said grinding step comprising the steps of providing a first grinder arranged in parallel to one or more further grinders, splitting an incoming batch of material to be ground into at least first and second portions, said first portion being fed to said first grinder and said second portion being fed to at least one of said one or more further grinders, determining the process time taken for said first grinder to grind said first portion and determining the process time taken for said at least one of one or more further grinders to grind said second portion, and adjusting the ratio of said first and second portions in a subsequent batch as a function of the difference between the process time taken for said first grinder to grind said first portion and the process time taken for said at least one of one or more further grinders to grind said second portion of one more batches in order to minimise said difference in process times for the grinding of the first and second portions of subsequent batches.

The first portion of the incoming batch of material may first be fed to said first grinder as a first sub-batch and said second portion (i.e. remainder of the incoming batch) may be subsequently fed to said at least one of said one or more further grinders as a second sub-batch.

The method may comprise using a mechanical device to split said incoming batch into said first and second portions at a selected ratio. For example, said mechanical device may comprise a conveyor adapted to deliver said first portion of the incoming batch to said first grinder and subsequently deliver said second portion of the incoming batch to said one or more further grinders as a second sub-batch. The conveyor may comprise a screw conveyor having a closable opening in a side wall thereof through which said first portion of the incoming batch is delivered to said first grinder, the method comprising closing said opening to subsequently deliver said second portion (i.e. remainder) of the incoming batch to said one or more further grinders as a second sub-batch via an end of the screw conveyor or a further opening in the side wall thereof, wherein the ratio of said first and second portions is adjusted by controlling the timing of the closure of the opening.

In one embodiment the method may comprise the step of configuring the first grinder such that said incoming batch is selectable from a feed batch of at least one of a plurality of grinders or sets of grinders of a compounding mill, such that said at least one of said plurality grinders or sets of grinders comprises said one or more further grinders.

Preferably the method comprises the step of recombining said first and second portions downstream of said first and one or more further grinders and upstream of a mixing step.

The method may comprise a blending step for blending ingredients to form said animal feed, said blending step comprising a weighing step, said grinding step and a mixing step.

The method may further comprise adding liquids to the ingredients in said mixing step downstream of said grinding step.

Preferably the method further comprises a conditioning step downstream of said mixing step, wherein the blended ingredients are conditioned by the application of heat. Said application of heat may be achieved by supplying steam to the ingredients.

The method may further comprise a pressing step downstream of said conditioning step, wherein the resulting animal feed is pressed into pellets. The pressing step may comprise extruding said animal feed through one or more dies or through a nip at a downstream end of a screw press. Preferably the animal feed is cooled downstream of said pressing step. The animal feed may be coated with an oil, such as vegetable oil, downstream of the pressing step.

According to a further aspect of the present invention there is provided an apparatus for preparing animal feed comprising a first grinder, one or more further grinders arranged parallel to said first grinder, means for splitting an incoming batch of material to be ground into at least first and second portions at a selected ratio, wherein said first portion is fed to said first grinder and said second portion is fed to at least one of said one or more further grinders, determining means for determining the process time taken for said first grinder to grind said first portion and determining the process time taken for said at least one of one or more further grinders to grind said second portion, and control means adapted to control the splitter means to adjust the ratio of said first and second portions in a subsequent batch as a function of the difference between the process time taken for said first grinder to grind said first portion and the process time taken for said at least one of one or more further grinders to grind said second portion of one more batches, thereby minimising said difference in process times for the grinding of the first and second portions of subsequent batches.

The splitter means may comprise a mechanical device configured to split said incoming batch into said first and second portions at a selected ratio. In one embodiment the mechanical device may comprise a moveable wall or diverter plate in a flow passage carrying said incoming batch. Alternatively the mechanical device may comprise a conveyor adapted to deliver said first portion of the incoming batch to said first grinder and subsequently deliver said second portion of the incoming batch to said one or more further grinders as a second sub-batch. In one embodiment the conveyor may comprise a screw conveyor including a closable opening in a side wall thereof operable to deliver said first portion of the incoming batch to said first grinder, said second portion (i.e. remainder) of the incoming batch being delivered to said one or more further grinders as a second sub-batch via a distal end of the screw conveyor when said opening is closed. The ratio of said first and second portions may be adjusted by controlling the timing of the closure of the opening.

The splitter means may deliver said first and second portions of the incoming batch to respective feed hoppers upstream of said first and at least one of said one or more further grinders.

The first and one or more further grinders may comprise rotating hammers or beater bars acting against a grinder screen or mesh.

In one embodiment there is provided a plurality of grinders or grinder sets, the first grinder being reconfigurable such that said incoming batch is selectable from a feed batch of at least one of said plurality of grinders or grinder sets, such that said at least one of said plurality of grinders or grinder sets comprises said one or more further grinders.

A blending process may be provided for blending ingredients to form said animal feed, said blending process comprising a weighing step, a grinding step and a mixing step, wherein said grinding step comprises said first grinder and said one or more further grinders.

Preferably means are provided for adding liquids to the ingredients in said mixing step downstream of said grinding step.

A conditioning process may be provided downstream of said blending process, wherein the blended ingredients are conditioned by the application of heat. For example, a boiler may be configured to add steam to the ingredients to heat the ingredients.

The apparatus may further comprise a pressing process downstream of said conditioning step, wherein the resulting animal feed is pressed into pellets by extruding said animal feed through one or more dies or through a nip at a downstream end of a screw press.

The apparatus may further comprise means for coating the animal feed with an oil, such as vegetable oil, downstream of the pressing step.

BRIEF DESCRIPTION OF THE DRAWINGS

A method and apparatus for preparing animal feed in accordance with embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which :Figure 1 is a schematic view of an apparatus for preparing animal feed in accordance with an embodiment of the present invention; and

Figure 2 is a schematic view of a screw conveyor when used as a splitter device for splitting an incoming batch of animal feed into first and second portions or subbatches.

DETAILED DESCRIPTION OF THE DRAWINGS

As schematically illustrated in Figure 1, a method and apparatus for preparing animal feed in accordance with an embodiment of the present invention comprises a weighing step 2, a grinding step 6,8 and a mixing step 10 for feed materials, typically comprising vegetable matter, followed by a conditioning step 14, a pressing step 16 and a cooling step 18.

In the weighing step 2, specified quantities of bulk solid raw materials may be dropped from bulk storage silos, preferably via screw conveyors with sufficient gradient to guarantee good emptying, into one or more load cell mounted hopper scales. The scales may be adapted to weight incoming batches between 1kg and 50kg or between 30kg to 3T to suit the amounts of each ingredient required. The weighed out raw materials may be transferred into dedicated pre-grinder bins.

Bulk liquid raw materials may be pumped from respective bulk storage tanks using dedicated pumps and process lines and added to the work in progress, or ‘mix’, as required.

Packed raw materials are either weighed out manually using weigh scales or prefilled into micro-ingredient bins and automatic weighing systems.

Medicinal additives may be automatically added, for example via a dedicated carousel unit, on a closed loop to mixers, enabling accurate additions to be made. Medicinal additives required in smaller quantities may be added manually. The manually weighed out raw materials may be added to the mix via a dedicated entry point.

The consumption of these licensed raw materials may be recorded in a register to facilitate subsequent verification of the materials and quantities consumed.

In order to ensure the homogeneity of the finished product and to produce the physical attributes required, the cereal raw material ingredients are ground in one or more grinders in a grinding step prior to being conveyed into a batch specific top hopper of a mixing plant in a mixing step.

Typically the batch grinding process is the slowest step in the animal feed production process. Therefore to avoid the creation of a bottle neck in the system two or more grinders 6,8 may be provided arranged in parallel, typically referred to as grinder sets, wherein an incoming batch of material to be ground is split into separate sub-batches to pass through each grinder of the set, or subsequent incoming batches may be fed to each grinder consecutively, the ground material being recombined downstream of the grinders of the grinder set. However, a problem with this arrangement is that the grinders may not all operate at the same efficiency as each other. Therefore simply splitting the incoming batch into equal portions may lead to one of the grinders in a grinder set taking longer to grind its portion of the batch that the others, causing delays in the system. It is also known to provide parallel arranged grinders sets, each comprising a plurality of parallel arranged grinders, wherein subsequent incoming batches may be fed to each grinder set consecutively. Again, differences in overall process time between each grinder set can cause delays in the overall production process.

In accordance with an embodiment of the present invention there is provided a control system including an adjustable splitter device 4 upstream of a plurality of parallel grinders or grinder sets 6,8 (two shown in Figure 1), whereby the relative size of each portion or sub-batch of an incoming batch supplied to each grinder or grinder sets (group of two or more parallel grinders), may be adjusted. The control system includes means for determining the process time for each grinder or grinder set to complete a grinding operation on a respective portion or sub-batch of the incoming batch, for example by sensing the arrival of the respective portion or subbatch as it enters the respective grinder or grinder set and sensing the arrival of material from each grinder or grinder set at the subsequent mixing step and timing the interval between the two occurrences, wherein the control system is programmed to compare the process time for each grinder or grinder set and to adjust the splitter device 4 to adjust the relative size of each portion of a subsequent batch supplied to each grinder 6,8 or grinder set to minimise the difference in the process time between them.

By monitoring the process time of each grinder or grinder set and, based thereon, adjusting the splitter device to adjust the proportion of material supplied to each grinder or grinder set in subsequent batches, the effect of any fall off in performance of a particular grinder or grinder set on the overall time required for the grinding process to be completed can be minimised.

As illustrated in Figure 2, the incoming batch from the weighing step 2 may be conveyed to the grinders or grinder sets 6,8 of the grinding step by a conveyor, preferably a screw conveyor 20. The splitter device 4 may configure the conveyor to deliver a first portion or sub-match of the incoming batch of material to the first grinder or grinder set and subsequently deliver a second portion or sub-batch (i.e the remainder of the incoming batch) to the second grinder or grinder set. Where the conveyor comprises a screw conveyor, the splitter device 4 may comprise a selectively closable opening 22 in a side wall of the screw conveyor 20 for delivering the first portion or sub-batch of an incoming batch or material to a feed hopper of a first grinder or grinder set 6, said opening 22 being closed to deliver the second portion of sub-batch (i.e. the remainder of the incoming batch) to a feed hopper of a second grinder or grinder set 8 via a distal end of the screw conveyor 20. The timing of the closing of the opening 22 in the side wall of the conveyor 20 may be adjusted to adjust the size (weight or volumetric) ratio between the first and second portions of the incoming batch of material that are fed to the first and second grinders or grinder sets 6,8.

In one embodiment an additional grinder may be provided arranged in parallel to one or more existing grinders or grinder sets, a portion of the incoming batch normally supplied to the one or more existing grinders or grinder sets being separated by said splitter device such that the additional grinder can reduce the overall process time of the mill by reducing the time required by the grinding step of the blending process. The process time of the additional grinder may be compared to the process time of the one or more existing grinders or grinder sets and the resulting time difference may be used by the control system to adjust the proportion of subsequent batches of material separated by the splitter device and supplied to the additional grinder to optimise the overall time of the grinding step.

It is envisaged that the additional grinder may be reconfigurable to be coupled in parallel to different sets of grinders (i.e. groups of grinders arranged in parallel to one another for grinding a common incoming batch of material) in the feed production plant, for example in parallel blending lines, where additional grinding capacity is required, to increase the adaptability of the mill.

Each grinder may comprise an electrically driven grinder, operating within a sealed enclosure, adapted to grind the material to a uniform particle size. In a preferred embodiment, rotating hammers within each grinder break down the raw materials and force them through a mesh. Variation in rotation speed and mesh size allow different products to be processed, as required (e.g. fast and fine for pellets and slow and coarse for meals).

Each grinder may be mounted above a respective collection hopper which may be vented via a reverse jet bag filter dust abatement unit which discharges to within the process buildings. Once ground, the batch of material in the collection hoppers is conveyed to the mixing step top hopper by means of enclosed conveyors.

From the top hopper the materials are gravity-fed into a batch mixer (schematically shown by reference number 10 in Figure 1). Mixers may be dedicated to specific product types (e.g. ruminant and monogastric formulations) to prevent cross contamination. At this stage of the process, the low inclusion ingredients (representing typically 5% of the product mass), such as vitamins, trace materials and medicinal additives, may be added directly into the mixer via feed lines 12. Depending upon the recipe, liquid additives, such as oils, can be weighed and added into the mix via dedicated lines at this stage.

The mixing may be performed within a horizontal enclosed continuous mixer. Two horizontal enclosed continuous mixers may be arranged sequence to improve process speed. The residence time for the mixing process is typically three to four minutes prior to despatch into a bottom hopper. When the mixing cycle is complete the homogeneous batch is conveyed for further processing in the conditioning and pressing steps. However, if a meal product is being produced, the batch may be either be transferred directly from the mixer to a finished product bin (if no heat treatment is required) or may be passed to the heat treatment line (conditioning step) for further processing.

The mixing step of the method is in an area in which tight controls and procedures are preferably employed, to prevent cross contamination, which can occur as a result of a batch of blended feed or raw material picking up traces of feed or raw material left behind by the previous batch. Production may be planned to sequence batches of medicated feed together, ensuring that the sequencing of production runs does not lead to cross contamination issues. When this is not practical, the processing system may be purged with a small batch of raw materials (such as non medicated cereal) known as a ‘flush batch’ or ‘clean-out batch’, to ensure that all traces of medicated additives are removed from the process lines and mixer. This flush batch may be incorporated in a finished batch of product in accordance with the relevant code of practice.

A conditioning step 14, comprising heat treatment of the feed product, may follow the mixing step 10. In the conditioning step steam may be directly added into the mix to raise its temperature so that any bacteria present (such as salmonella) are eradicated. The steam also improves the ‘workability’ of the mix in preparation for the subsequent pelleting process in the pressing step. Steam may be supplied from a boiler and passed into the mix through insulated lines. At this stage, further materials (such as molasses) may be added as required. Batches may undergo short term and long term conditioning, short term conditioning having a residence time of approximately 10 seconds and long term conditioning (LTC) having a residence time of approximately several minutes, dependant on LTC size and press throughput. During the conditioning step the mix may typically absorb between 1 and 4% by weight of moisture.

After conditioning the hot mix is preferably conveyed to a respective press line of the pressing step 16.

Two types of pressing may be carried out, namely standard pressing, where the pellets are produced by passing the mix into a press and extruding it through ring dies, or BOA compaction, where the pellets are produced by extruding the mix through a nip at the end of a screw conveyor prior to second pressing in a standard press. Varying the processing parameters, including nip and die dimensions and press rotation speeds facilitate the production of different pellet sizes, to meet specific product requirements.

After pelleting in the pressing step the hot product may then be passed through a counter flow air cooler 18 in a cooling step to reduce its temperature, causing it to harden and become durable. The cooling process preferably involves air at ambient temperature being passed directly over the pellets or nuts, either in vertical towers or over trays of feed in rotary coolers. Waste air generated throughout this part of the process may be ducted into a respective cyclone to remove dust and may then be vented to atmosphere. The dust collected may be recycled into production.

At least a portion of the resulting feed product may be crumbed to produce feeds for specific animals, such as piglets and chickens. Crumbing is the process of passing pelleted product through the nip between a set of counter rotating rollers within an enclosed system to produce a smaller product known as a crumb.

Approximately 95% of the processed pellets and crumb may be conveyed into an enclosed coater into which vegetable oils may be sprayed via meters onto the product.

Product despatch may be conducted in several outloading bays. Bulk vehicles may be positioned on a weighbridge below a conveyor discharge system.

Non-medicated products may be conveyed from finished product holding bins via a screen to remove extraneous dusty matter, to an appropriate discharge pipe and 10 into the vehicle for delivery to the customer. Medicated products, however, may be conveyed from finished product holding bins to the vehicle without being screened and therefore are delivered to the customer with particulate matter, as a result of its associated medicinal additive content.

The invention is not limited to the embodiments described herein but can be amended or modified without departing from the scope of the present invention.

Claims

1. A method for preparing animal feed including a grinding step for grinding one or more ingredients, said grinding step comprising the steps of providing a first grinder arranged in parallel to one or more further grinders, splitting an incoming batch of material to be ground into at least first and second portions, said first portion being fed to said first grinder and said second portion being fed to at least one of said one or more further grinders, determining the process time taken for said first grinder to grind said first portion and determining the process time taken for said at least one of one or more further grinders to grind said second portion, and adjusting the ratio of said first and second portions in a subsequent batch as a function of the difference between the process time taken for said first grinder to grind said first portion and the process time taken for said at least one of one or more further grinders to grind said second portion of one more batches in order to minimise said difference in process times for the grinding of the first and second portions of subsequent batches.

2. A method as claimed in claim 1, wherein the first portion of the incoming batch of material is first fed to said first grinder as a first sub-batch and said second portion is subsequently fed to said at least one of said one or more further grinders as a second sub-batch.

3. A method as claimed in claim 1 or claim 2, wherein said method comprises using a mechanical device to split said incoming batch into said first and second portions at a selected ratio.

4. A method as claimed in claim 3, wherein said mechanical device comprises a conveyor adapted to deliver said first portion of the incoming batch to said first grinder and subsequently deliver said second portion of the incoming batch to said one or more further grinders as a second sub-batch.

5. A method as claimed in claim 4, wherein the conveyor comprises screw conveyor having a closable opening in a side wall thereof through which said first portion of the incoming batch is delivered to said first grinder, the method comprising closing said opening to subsequently deliver said second portion of the incoming batch to said one or more further grinders as a second sub-batch via an end of the screw conveyor or a further opening in the side wall thereof, wherein the ratio of said first and second portions is adjusted by controlling the timing of the closure of the opening.

6. A method as claimed in any preceding claim, comprising the step of configuring the first grinder such that said incoming batch is selectable from a feed batch of at least one of a plurality of grinders or sets of grinders of a compounding mill, such that said at least one of said plurality grinders or sets of grinders comprises said one or more further grinders.

7. A method as claimed in any preceding claim, comprising the step of recombining said first and second portions downstream of said first and one or more further grinders and upstream of a mixing step.

8. A method as claimed in any preceding claim, including a blending step for blending ingredients to form said animal feed, said blending step comprising a weighing step, said grinding step of any of claims 1 to 7 and a mixing step.

9. A method as claimed in claim 8, further comprising adding liquids to the ingredients in said mixing step downstream of said grinding step.

10. A method as claimed in claim 8 or claim 9, said method further comprising a conditioning step downstream of said mixing step, wherein the blended ingredients are conditioned by the application of heat.

11. A method as claimed in claim 10, wherein said application of heat is achieved by supplying steam to the ingredients.

12. A method as claimed in claim 10 or claim 11, further comprising a pressing step downstream of said conditioning step, wherein the resulting animal feed is pressed into pellets

13. A method as claimed in any of claims 12, wherein the animal feed is coated with an oil, downstream of the pressing step.

14. An apparatus for preparing animal feed comprising a first grinder, one or more further grinders arranged parallel to said first grinder, splitter means for splitting an incoming batch of material to be ground into at least first and second portions at a selected ratio, wherein said first portion is fed to said first grinder and said second portion is fed to at least one of said one or more further grinders, determining means for determining the process time taken for said first grinder to grind said first portion and determining the process time taken for said at least one of one or more further grinders to grind said second portion, and control means adapted to control the splitter means to adjust the ratio of said first and second portions in a subsequent batch as a function of the difference between the process time taken for said first grinder to grind said first portion and the process time taken for said at least one of one or more further grinders to grind said second portion of one more batches, thereby minimising said difference in process times for the grinding of the first and second portions of subsequent batches.

15. An apparatus as claimed in claim 14, wherein said splitter means comprises a mechanical device configured to split said incoming batch into said first and second portions at a selected ratio.

16. An apparatus as claimed in claim 15, wherein the mechanical device comprises a conveyor adapted to deliver said first portion of the incoming batch to said first grinder and subsequently deliver said second portion of the incoming batch to said one or more further grinders as a second sub-batch.

17. An apparatus as claimed in claim 16, wherein said conveyor comprises a screw conveyor including a opening in a side wall thereof openable to deliver said first portion of the incoming batch to said first grinder, said second portion of the incoming batch being delivered to said one or more further grinders as a second sub-batch via a distal end of the screw conveyor or a further opening when said opening is closed.

18. An apparatus as claimed in claim 17, wherein the ratio of said first and second portions is adjusted by controlling the timing of the closure of the opening.

19. An apparatus as claimed in any of claims 14 to 18, wherein the splitter means is configured to deliver said first and second portions of the incoming batch to respective feed hoppers upstream of said first and at least one of said one or more further grinders.

20. An apparatus as claimed in claim 15, wherein said mechanical device comprises a moveable wall or diverter plate in a flow passage carrying said incoming batch.

22. An apparatus as claimed in any of claims 14 to 20, wherein said first and one or more further grinders comprise rotating hammers or beater bars acting against a grinder screen or mesh.

23. An apparatus as claimed in any of claims 14 to 22, comprising a plurality of grinders or grinder sets, the first grinder being reconfigurable such that said incoming batch is selectable from a feed batch of at least one of said plurality of grinders or grinder sets, such that said at least one of said plurality of grinders or grinder sets comprises said one or more further grinders.

24. An apparatus as claimed in any of claims 14 to 23, comprising a blending process for blending ingredients to form said animal feed, said blending process comprising a weighing step, a grinding step and a mixing step, wherein said grinding step comprises said first grinder and said one or more further grinders.

25. An apparatus as claimed in claim 24, further comprising a conditioning process downstream of said blending process, wherein the blended ingredients are conditioned by the application of heat.