GB2385897A

GB2385897A - Method and apparatus for forming a clay article

Info

Publication number: GB2385897A
Application number: GB0204730A
Authority: GB
Inventors: Russell Shane Kenworthy
Original assignee: Hepworth Building Products Ltd
Current assignee: Hepworth Building Products Ltd
Priority date: 2002-02-28
Filing date: 2002-02-28
Publication date: 2003-09-03
Also published as: GB0204730D0

Abstract

A method of forming an article from green clay comprises: (i) providing a first jointing surface situated on a first green clay element 1; (ii) providing a second jointing surface situated on a second green clay element 11; (iii) placing the said first and second jointing surfaces in mutual contact; and (iv) applying a vibratory motion to one of the elements. Preferably no sticking clay is employed between the jointing surfaces, and no epoxy-resin is painted onto the joint 15 formed. The article produced by the method may be a drainage component such as a pipe fitting, a chimney or roof furniture. Apparatus for use in the manufacture of a pipe fitting may comprise a mandrel 21 having a hollow core which contains a rotation member adapted to rotate about an axis generally parallel to the longitudinal axis of the core for causing vibration of the mandrel in a direction that is substantially radial relative to the mandrel.

Description

METHOD AND APPARATUS FOR FORMING A CLAY ARTICLE The invention relates to a method and apparatus for forming an article from green clay.

Particularly, but not exclusively, the invention relates to forming a drainage component, chimney or roof furniture from green clay.

Green clay has the advantage of being easy to deform plastically, whilst having sufficient strength to allow any object formed from the clay to be handled and transported without deleterious further deformation. Green clay is made up of a matrix of particles, with water located between the particles. The particles are are typically platelet shaped, interlock with each other, and are bound together by the hydrogen bonding of the water molecules, which form thin films between each platelet. The thickness of the water films is dependent on the water content of the clay; the wetter the clay, the thicker the films of water between each platelet, thereby allowing the platelets to move more freely over each other, resulting in a more plastic clay.

Once a green clay object is formed into the desired shape, it is typically left to dry slowly. During the drying process, the water between the platelets of the clay slowly diffuses to the surface, where it evaporates off, which hardens and embrittles the object.

Once evaporation drying is complete, the object is fired, which involves a partial vitrification of the platelets in the clay matrix to form a hard, glassy structure.

Taking the manufacture of a green clay pipe fitting as an example, the process is typically performed using a combination of preparation, sticking, and finishing procedures. In the formation of a junction, for example, the surfaces of the green clay elements to be joined together first need to be appropriately prepared, to allow a suitable joint to form. Conventionally, sticking clay or a suitable slip is applied to the surfaces to be joined, and the surfaces are placed in contact. Finishing steps are then required to remove any flash, and to smooth-out the junction. In the case of large clay junctions,

such as those of extruded green clay pipe sections, the joint may require painting with epoxy resin post-firing to impart the junction with the sufficient water-tightness.

Figure 4 illustrate a method used in the forming of a junction 17 according to the prior art. This process is typically performed manually by a skilled worker. The main section of the junction is the barrel 1 and the process adds an arm 11 to the barrel 1, at an oblique angle, to provide a branch.

Before the junction 17 can be formed, the surfaces to be joined need to be prepared.

The preparation steps are shown in Figure 4. Initially the barrel 1 is cut to length and a setting ring 5 is formed at one end. As shown in Figure 5, the barrel 1 is then placed horizontally on a wooden support bed 3. A tin sticking profile former (not shown) is placed on the top surface of the barrel 1, and a profiled hole 9 is cut into the barrel 1 with a bow wire (not shown), using the tin former as a guide. Water is applied to the profiled hole 9, which is then scratted with a suitable tool to create a rough surface which is then left to soak.

The arm 11 is also cut to length and a setting ring 13 is formed at one end. The arm 11 is next positioned vertically on a bench (not shown) and a tin sticking profile former (not shown) is positioned on the surface of the arm 11. A mounting profile 14 is cut onto the end of the clay arm 11 with a bow wire (not shown) using the tin former as a guide. The mounting profile is configured such that, when orientated correctly, it fits contiguously with the perimeter of the profiled hole 9 formed in the barrel 1. In the present example, the profiled hole 9 and mounting profile 14 are configured such that, when placed in a contiguous relationship, the arm 11 extends from the side of the barrel 1 at an oblique angle. This method is, however, used for a wide variety of other pipe configurations ; a T-junction being an example. Once the mounting profile 14 has been formed, water is applied to it and it is scratted with a suitable tool to create a rough surface.

After the preparation steps have been completed, the sticking process is commenced.

The first step of the sticking process is to position the arm 11 onto the pre-prepared barrel 1 with the edges of the profiled hole 9 and the mounting profile 14 directly addressing each other, such that the arm 11 and the barrel 1 form the required junction.

The positioning of the arm 11 and the barrel 1 is then consolidated by pushing and patting the arm 11 onto the barrel 1, with care taken not to distort either component. A peg (not shown) is next run around the external recess of the joint 15 formed at the junction of the mounting profile 14 and profiled hole 9, to fuse the arm 11 and the barrel 1 together. A bead of sticking clay (not shown) is also applied to the whole length of the external surface of the joint 15 and smoothly blended by hand into the comer of the joint 15. Pressure is then applied to the internal surfaces of the joint 15 using a wet rubber disk, to fuse the internal surfaces together.

The final part of the process comprises a series of finishing steps as shown in Figure 4.

Initially, the external surfaces of the joint 15 are smoothed with the wet rubber disk, and the internal and external surfaces of the joint 15 are finished by smoothing with a wet sponge. The junction 17 is then allowed to dry, and subsequently fired.

After drying, the junction 17 is fired and the joint 15 is painted with an epoxy resin, to decrease the porosity of the junction around the joint 15. This step also serves to impart the junction 17 with sufficient strength to prevent the arm 11 from becoming detached from the barrel 1 during transport and normal use.

The above method is very labour intensive and requires significant skill and experience - which affects the quality of the junctions produced, because the skills of different workers clearly tend to vary. The process described above is also time-consuming, because time is required for the sticking clay or slip to set, dry and harden.

It is a further disadvantage that the above method produces joints that are nonhomogeneous, with respect to the clay forming the body of the barrel 1 and arm 11.

This is largely the result of the slip or sticking clay being used in the formation of the joint 15, remnants of which will always remain. As a result, the joint 15 will always have different material properties to the bulk of the clay and, as such, potentially

provide a weak point in the junction 17. It is also likely that a joint produced by this prior art method would be of a higher porosity than the bulk of the clay.

In view of the foregoing, the present invention sets out to provide a method of consistently and efficiently forming homogeneous green clay articles, particularly chimneys, roof furniture and drainage components such as junctions, of sufficient strength. Furthermore, the invention sets out to provide a process which does not require the need for sticking clay or slip and which does not require the painting of the joint with epoxy resin post-firing.

Accordingly, a first aspect of the invention provides a method for forming an article from green clay, the said method comprising: (i) providing a first jointing surface situated on a first green clay element ; (ii) providing a second jointing surface situated on a second green clay element ; (iii) placing the said first and second jointing surfaces in mutual contact ; and (iv) applying a vibratory motion to one of the said elements.

Preferably, the said first and second jointing surfaces are prepared prior to placing them in mutual contact and this may involve a combination of applying water and scratting.

It is particularly preferred that one of the said elements is placed on a correspondingly configured member prior to the application of the said vibratory motion, and the said member provides the said vibratory motion.

Pressure may be applied to one of the elements, in such a direction that the first and second elements are urged together, whilst applying the said vibratory motion. The said pressure may be applied for a period of from 2 to 30 seconds. Preferably, the pressure is applied for a period of from 5 to 15 seconds.

It is particularly preferred that a slip or a sticking clay is not employed between the said first and second jointing surfaces. It is further preferred that an epoxy resin is not painted onto the joint formed at the jointing surfaces.

The article may be a pipe junction, the said first element a barrel section and the said second element an arm section. In such a case, it is preferred that the said member is a generally cylindrical mandrel and the said barrel section is placed substantially coaxially on the said mandrel prior to the application of the said vibratory motion.

The said vibratory motion may then comprise at least a component of reciprocating motion in a direction that is radial relative to the said mandrel.

According to a second aspect of the invention, there is provided a pipe fitting manufactured according to a method in accordance with the first aspect of the invention.

A third aspect of the invention provides apparatus for use in the manufacture of a pipe fitting according to the first aspect of the invention, the said apparatus comprising a mandrel comprising a hollow core, the said core containing a rotation member adapted to rotate about an axis generally parallel to the longitudinal axis of the said core, for causing vibration of the said mandrel in a direction that is substantially radial relative to the said mandrel.

Preferably, the said core further contains motor means for driving the rotation of the said rotation member.

It will therefore be apparent that a process according to the present invention has many advantages over the prior art process described above. Such a process can be simpler and is less dependent upon the skill of the worker, which leads to a greater consistency of components produced. A process according to the present invention can also lead to a shorter manufacturing time than the prior art process. This is the result of both a generally simpler process, and the fact that no slip or sticking clay need be used, and hence no time need be allowed for the slip or sticking clay to set. The processing time is further reduced because there is no need to paint the joint with epoxy resin postfiring. It is a further advantage that a process according to the present invention lends itself to automation, due to its increased simplicity. This inevitably leads to large increases in efficiency and reduced labour.

It is a further advantage that the green strength of the articles produced by a process according to the invention is greater than those produced by the prior art process described above. The joints formed using the process according to the present invention are homogeneous and have the same porosity as the remainder of the component. As a result of the higher green strength, green clay components produced by the process according to the present invention are associated with lower scrap rates. This is predominantly because such components are less likely to fall apart during drying or firing than components of a lesser green strength produced by the process according to the prior art.

A process according to the present invention also has advantages in that materials can be saved, relative to the prior art process. In particular, the lack of the need for a sticking clay, slip, or epoxy paint in the present process leads to cost savings.

For a better understanding of the invention, an embodiment of a process for forming a junction in accordance with the invention will now be described with reference to the accompanying drawings in which :- Figure 1 is a flow diagram detailing preparation, sticking and finishing steps of a process for forming a green clay junction in accordance with the invention; Figure 2 is a perspective, schematic view of a vibration rig for use in a process according to the present invention, the apparatus being shown in conjunction with a barrel; Figure 3 is a side view of the vibration rig of Figure 2, shown in conjunction with a formed junction; Figure 4 is a flow diagram illustrating preparation, sticking and finishing steps of a process for forming a green clay pipe junction in accordance with the prior art; Figure 5 is a side view of an extruded green clay barrel section being prepared as part of a process for forming a junction in accordance with the prior art; and

Figure 6 is a side view of a green clay pipe junction formed according to the prior art.

Figures I illustrates a process for forming a pipe junction 17 according to the present invention. The preparation steps are similar to those described above in relation to the prior art process shown in Figure 4, with the exception that the wetting and scratting steps are omitted for both the barrel I and the arm 11. Surface preparation steps such as these can optionally be included, but subsequent steps in the process can mean that they are not required.

After preparation, the barrel 1 is slid onto a mandrel 21. The mandrel 21 is part of a vibration rig 19 and this is shown in Figure 2. From this figure, it will be seen that the mandrel 21 is generally cylindrical and projects substantially horizontally from a support portion 23 of the rig 19. In this case, the support portion 23 merely supports the mandrel 21 and allows power to be supplied to a motor (not shown) located inside the mandrel 21. The drive shaft of the motor is eccentrically connected with a weight, so that a radially vibrating motion is imparted to the mandrel 21 when the motor runs.

Many variations are possible of the mandrel itself, the support for it and the precise nature of the vibration inducing mechanism.

It is also the case that the mandrel could be replaced by a member having a different shape-this being particularly so if the fitting being formed has a significantly different shape from the junction described above.

The barrel 1 is slid onto the mandrel 21 up to an end stop, such that the profiled hole 9 faces generally upwards. The outer diameter of the mandrel 21 is of such a size that it fits quite closely with the radially inner surface of the barrel 1. The sticking stage is commenced by arm 11 being positioned onto the barrel 1 with the perimeteral surfaces of the profiled hole 9 and the mounting profile 14 in direct contact. In this position, the arm 11 naturally settles into its eventual position relative to the barrel 1 in the final product.

Figure 3 is a side view of the vibration rig 19, showing the arm 11 positioned on the barrel 1 as described above. A support tray 22 is shown in position beneath the underside of the barrel 1. The support tray 22 is raised to this position in order to support the barrel and prevent spreading at the bottom of the joint 15 between the two elements. The tray 22 is configured to fit very closely against the radially outer surface of the barrel 1.

The mandrel 21 is vibrated for a period of from 5 to 15 seconds, whilst the arm 11 is manually held in position. The vibratory motion acts substantially in a radial direction relative to the mandrel 21 and has the effect of fusing the green clay of the barrel 1 and the arm 9 together along the joint 15, to produce a homogeneous green clay junction 17.

The vibration period of from 5 to 15 seconds has been found particularly effective in the formation of this particular article. However, other periods can be just as suitable for different, or even similar, products, although 2 to 30 seconds have been found particularly effective for most applications.

The junction 17 produced by this method does not require the use of a sticking clay or slip, because the vibration action produces a joint 15 of sufficient green strength without this.

After the vibration step the junction 17 is slid from the mandrel 21 and placed on a wooden support block (not shown). The finishing stage is then commenced by the internal and external surfaces of the joint 15 being wiped with a wet rubber disk and then with a wet sponge.

The barrel 1 is subsequently stamped before being set on a palette. A taper plug (not shown) is inserted into the end 7 of the barrel 1 that is not provided with the setting ring 5, in order to remove ovality. Once this has been done, the junction 17 is left to dry, before being fired.

In contrast to the junctions produced by the above-described method according to the prior art, the joint 15 has sufficient green strength to prevent the arm 9 from falling off

during either the drying or firing process. Furthermore, the junction 17 does not require the joint 15 to be painted with epoxy resin post-firing, because the clay forming the joint 15 is homogenous and has the same porosity as the clay of the barrel 1 and arm 9.

Although having clear and particular benefits in the manufacture of pipe junctions, it is emphasised that the invention is not limited to the formation of junctions and may be employed with just as much success in the manufacture of a wide range of other articles, as described above.

Claims

CLAIMS:

1. A method for forming an article from green clay, the said method comprising: (i) providing a first jointing surface situated on a first green clay element; (ii) providing a second jointing surface situated on a second green clay element ; (iii) placing the said first and second jointing surfaces in mutual contact; and (iv) applying a vibratory motion to one of the said elements.

2. A method according to Claim 1, wherein one or both of the said first and second jointing surfaces are subject to a preparation step prior to being placed in mutual contact.

3. A method according to 2, wherein the said first and second jointing surfaces are prepared by a combination of applying water and scratting.

4. A method according to any preceding claim, comprising applying pressure to one of the said elements in such a direction that the said first and second jointing surfaces are urged together, whilst applying the said vibratory motion.

5. A method according to Claim 4, wherein the said pressure is applied for a period of from 2 to 30 seconds.

6. A method according to Claim 5, wherein the said pressure is applied for a period of from 5 to 15 seconds.

7. A method according to any preceding claim, wherein one of the said elements is placed on a correspondingly configured member prior to the application of the said vibratory motion, and the said member provides the said vibratory motion.

8. A method according to any preceding claim, wherein a slip or a sticking clay is not employed between the said first and second jointing surfaces.

9. A method according to any preceding claim, wherein an epoxy resin is not painted onto the joint formed at the jointing surfaces.

10. A method according to any preceding claim, wherein the said article is a pipe junction, the said first element is a barrel section and the said second element is an arm section.

11. A method according to Claim 10, wherein the said member is a generally cylindrical mandrel and the said barrel section is placed substantially coaxially on the said mandrel prior to the application of the said vibratory motion.

12. A method according to Claim 11, wherein the said vibratory motion comprises at least a component of reciprocating motion in a direction that is radial relative to the said mandrel.

13. A method of forming a pipe fitting substantially as hereinbefore described with reference to any of figures 1 to 3 of the accompanying drawings.

14. A pipe fitting manufactured according to a method according to any of Claims 1 to 12.

15. A pipe fitting substantially as hereinbefore described with reference to any of figures 1 to 3 of the accompanying drawings.

16. Apparatus for use in the manufacture of a pipe fitting according to a method as set out in any of claims 1 to 13, the said apparatus comprising a mandrel comprising a hollow core, the said core containing a rotation member adapted to rotate about an axis generally parallel to the longitudinal axis of the said core, for causing vibration of the said mandrel in a direction that is substantially radial relative to the said mandrel.

17. Apparatus according to Claim 16, wherein the said core further contains motor means for driving the rotation of the said rotation member.