CA1189371A - Applying marking materials to surface - Google Patents

Abstract

ABSTRACT

APPLYING MARKING MATERIALS TO SURFACES

A method and apparatus for marking road surfaces, runways etc. Marking material, normally a heat fusable solid in particulate form, is passed from a hopper (10) into a duct (18) where it is mixed with hot pressurised gas from a burner (20), the heat from the gas causing the marking material to partially melt. The marking material is then directed along a flight tube (22) from which it is expelled onto the surface (24) being marked. When the material cools the particles fuse together leaving a durable marking on the road surface. The apparatus is mounted on a vehicle (80) in such a way that markings may be applied on either side of the vehicle.

Control of the flow of marking material is by variable aperture venturi valves (40), as is control of flow of pigment and, when necessary, of purging material.

Description

This invention is concerned ~it~ improvements in or relating to marking surfaces and is particularly concerned with an improved apparatus for applying marking materials to a road surface.
Various methods and means of applying marking materials to surfaces such as highways and airport runways are known. These include methods in which a supply of the marking material is preheated to melt a constituent of the material and is then applied to a surface to be marked by passing through insulated pipes to an applicator. This method suffers the drawback that it involves a high capital outlay on the apparatus for heating the marking material in buIk and maintaining it at an appropriate temperature until it is applied. This is usually done by employing two vehicles one carrying the bulk supply of material and the other the applicator apparatus, although one large vehicle may suffice.
Other methods are known, for example as described in British patents 1,087,031 and 1,234,601 in which the surface to be marked is preheated and the marking material is then melted by contact with the surface. Some preheating oE the material may take place but the melting of the material takes place by contact with the surface. This method again involves the use of complicated apparatus and is also limited in the materials which may be employed. The heat softenable constituent of the marking material must be chosen with a sufficiently low melting point to ensure that it is satisfactorily melted by con~act with the preheated surface.
Devices for spraying particulate materials to form coatings on substrates are also known and include flame spray devices or apparatuses which are normally used to apply coatings of refractory material and the like.

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In such flame spray devices for example as shown in British patent 1,109,481 it is usual for the particulate material to be subjected to the direct efect of a flame. This has the disadvantage that, where materials with low melt temperatures are subjected to the direct eEfect of the flame, great care has to be taken to ensure the accuracy of the residence time of such materials ln the flame if charring of the materials is to be avoided. On the other hand, in arrangements where high melt temperature materials are usbjected to the heating effects of combustion gases there often has to be some additional heat supply in order to achieve the desired results. For example, in United Kingdom Patent Specification Nos. 1,087,031 and 1,234,~01 pre-heating of the highway surface to between 150F and 500F is advocated.
The invention, as herein broadly claimed, pro-vides an apparatus for applying to a road surface, marking material which is fusible onto the surface, the apparatus comprising means to burn a gaseous fuel in air under pressure to provide a supply of heated pressurized gas, duct means to direct the hot gas onto the road surface to be marked and means to inject a supply of marking material in unfused form into the hot gas stream -within the duct means downstream of the burner means,thereby to cause the marking material to impinge on the surface, characterized in that the duct means comprises a first elongate mixing chamber portion down which the hot gas is directed and into which the marking material is injected and a second elongate outlet duct portion co-axi~l with and downstream of the first portion, the outlet duct portion being of rectangular cross-section and having a ratio of length to maximum cross-sectional dimension of at least ~.75:1 so that the distance of the point of injection of the marking material from the road

- 2 -surface to be marked is such that at least some of the markin~ material is fused before the marking material impinges on the surface.
The outlet duct preferably includes a baffle which extends longitudinally of the duct.
In one preferred embodiment, the injection means for the marking material comprises a container for the material~at least one supply line connecting the container to the mixing chamber portion and means for supplying compressed gas to the container to entrain the material and carry it through the supply line.
Conveniently, the apparatus may comprise means for supplying purging material under pressure to the supply line to clear the supply line and duct.
The gaseous fuel may also be ignited, in a preferred embodiment, in a flashback burner and burn as it is passed through a combustion chamber, producing a resultant stream of hot gas. The gaseous fuel may be liquified petroleum gas.
The invention also includes a road marXing vehicle comprising a self-propelled chassis and an apparatus, as described above, having two ducts, and associated with each duct a burner and a supply line, both supply lines feeding from a common container and in which the supply lines, burners and ducts are rigidly mounted on the container such that one duct faces the road surface on each side of the container.
The method applied for marking the surface with a marking material may comprise, or provide at elevated temperatures, a màterial which is fusible.
It may involve the steps of burning a gaseous fuel in air under pressure to provide a supply of heated pres-surized gas, directing this supply of gas onto the surface to be marked,injecting a supply of marking material in unfused form into the hot gas stream and ,~

?371 thereby causing the matPrial to impinge on the su.rface, and maintaining the temperature of the hot gas stream and the distance of the point of injection of the marking material from the surface throughout the marking process such that at least some of the material is fused before the marking material impinges on the surface.
The material is preferably in particulate form and may be fluidized before injection into the hot gas stream. Preferably the marking material is injected into the hot gas stream in a reducing atmosphere. The method is particularly suitable for applying markings to highways and runways and the like.
A preferred embodiment of the invention will now be describedr by way of example, with reference to the i~cc~

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Figure 1 is a side view of a vehicle fitted with the apparatus for applying marking material o~ the present invention~
Figure 2 is a plan view of the vehicle and apparatus shown in Figure l;
Figure 3 is a diagrammatic representation of the spraylng : . :
apparatus;
..Figure 4 is a diagrammatic representation of an alt~rnative appara~us incorporating a gravity feed arrangement or }O. feeding part.iculate material; ; :
. Figure 5 and 6 each show front and side views of alternati~e configurations of a flight tube for use in the.apparatus . : I
of Figures 1 to 4 , Figure 7 shows twa views, side and plan, of a gas deflectox -for attachment to a flight tu~e of the~apptara~,w~
Figure 8 shows a~burner and swirl chamber in section; and Figure 9 shows a further configuration of flight-tube wi~h a : variable geomstryO

Apparatus us`ed hitherto, for the application of markings, , ~ .
` to highways er airport runways, etc., has not always 'i ` resulted in a well defined-durable marking at an acceptable speed~of application or an acceptable cost per unit area - covered-by the markin~gO.

The apparatus shown in t~le drawings enables`-a layer . : ; of a marking -material to be -sprayed onto ~a--high~

- - way, airvort ~ :runway or the liker wit~ great economy -- - . 1!
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. in mat~rial usage, at low power consumption and with minimum interruption of traffic flowO
Referring first to Figure 3, the apparatus comprises a bulk storage hopper 10 from which particulate marking materizl 11 may be fed via a screw elevator 12 to a fluidised bed feed device 14 and then via a line 16 to a mixing tube 18 where the material 11 is injected into a hot gaseous jet, created b~ a buxner 20, before passing along a duct or - fl~ght tube 22 to.be sprayed onto a hL~ghway 24, as shown at 26, to form a marking on the highway 24. The material is injected into a reduced atmosphere. The bulk storage hopper 10 is fed with compressed air from compressor 34 v1a a line 33 and control valve 31,so that the marking material 11 forms a fluidised bed. The hopper 10 can usefully have.a . capacity of between one and six tonnes dependi~g upon the ~ -size of vehicle on which the novel apparatus is to be-used.
The screw elevator 12 ideally has a feed rate of between one and fifteen lit.res per minute and feeds the particulate . marking.material via a duct 13 to the feed device 14. The feed device 14 has a capacity for 200 kilos of the particulate material fed thereto and comprises a container 30 fed with compressed air to form a fluidised bed. The compressed air is fed f~om compressor 34 via a line 33 and control valve 32 into the base of the container 30.
Material in the container 30 is ideally maintained at a . ~ . .

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level indicated b~ the dotted,line 35. A level switch 36, , provided on a side wall 37 of the contalner 30, is connected to a motor 38 where~y rotation of the screw elevator 12 ls e~fected in response to movement of a float member 39 , forming part of the valve 36. The feed device 14 also comprises a venturi valve 40 connected to the line 16 inside the containc~ 30 which valve 40 is controlled by an ..
actuator ~1 whereby the rate o~ reed of particulate material through the valve 40 may be adjusted or shut-off as requiredO
The actuator 41 is in turn conlrolled pneumatically, via a solenoid controlled valve 42, from an appropriate control - .- . . . . . ~
console 72 which may be mounted at any convenient location.
The disposition of the venturi valve 40 and the line 16 within the container 30 is consistent with obtaining a:
~, 15 flow of the particulate material which is of an acceptable range o~ ~article sizes,i.e. the particulate material will only show small diversities in size over a given period.
This is achieved by positioning the valve 40 and line 16 at an optimum le~el within the container. This occur~
20 because the'effect of the fluidised bed 14 is ~o strati~y ~ , -: :
, ~he particulate,material in the container 30 according to , the~size of granule. Large granules,will ~e more prevalent - towards the top of the co~tainer and small granules towards the bot_om.' Thus, at an cpti~u~ level the ideal si~e range of granule can he expected.
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On the outlet ~ide or the line 16 between the container and ~he mi~in~ t~c 13 thc~e is shown a pigment feed hopper 44 1; -, : -~l~L8~3~
r~e ~ T-_ ~.n ~ lternative arrangement there may .' .. L ~wo cr ~ore hoppers 44 and switching ,~f applopriate v~ ri va.v~s loc~ted within the hoppe~_ 44 enahle~
thc des1red pi~ment to be fed into the flow of particulate material in the line 16. There n~ay be spaced along line 16 c n~ber c~ annular passages for cool~ng the i_.
~ hc m;Ying tube 18, see Figure 3, is provided by a tc~ .ar chambe-, 46 of circular cross section connected at ..n upper end portion 47, thereof to a combustion chamber 48.
~he: combustion chamber 48 is in turn connected to the outlet 9 of the burner 20, see Figure 8.

1~ c bu-ner ~0 may be a commercially available flash back burner using liquid propane gas and air mi~ture as fuel.
~:,e ,_ir is su~plied via a line 52 fro~ the compressor 3a and ~he ~as i~ supplied via lines 53 from liquid petroleum 5a_ stora~e tanks 54, see Figure 3. A s~ark generator 55 is provided to initially ignite this fuel mixture.
The ~rran~ement is such that a mixture of air and ;:.(;..;c is coial-usted in th~ flash back burner 20 and the ~,~c; produced as a jet are prevented from oscillating - t~ ~u~r hy passing the gaseous jet through the swirl chamber 4~ as showll in Figure 8~ This .cc~bustion cha~her oonsists of two coa~ial cylindrical tubes 57 and 59. The inner tube 57 has ~ o rings of ports 58, which allow the air, fed via line 51 into the passage between tubes 57 and 59, to pass in~o tube 57 to react with a!'y unreacted fuelO These ports 58 are set at. an angle, as shown, so as to introduce the air into tuhe 5/ wit.h a co~ponent of velocity in the direction of the geneLal vt~locity OI the. gases already in the tube.

At the lower end portion 56 thereof the mixing tube 1~ is connected to the flight tube 22 by a suitable adaptor, not shown.
The length of the flifht tube 22 is chosen so that the particulate material, which i.s admixed with the hot gaseous jet in the mixing chamber 18, will remain in the flight tube for a sufficient time for enabling suffici.ent heat transfer from the gaseous jet to a heat softenable portion of the particulate material to substantiall~ liquify said portion.
In the arrangement shown diagrammatically in Figure 3 the ratio of the lenght of the tube 22 to its maximum cross-sectional dimention (width) is approximately 6.5:1. However, in other arrangements the tube 2~ may have a length to width ratio of between 2:1 and 30:1. The actual dimensions of the flight tube 22 will be chosen to suit the application, the particulate material, the feed rate of particulate material and the capacity of the burner 20.
Thus, in Figure 5 and 6 there are shown two further flight ~ 20 tubes 22a and 22b having length: width ratios of 9:1 and 4.75 1 respectively.
The flight tube 22 is also shaped to give a lamella flow of particulate material therefrom. Thus; as can clearly be seen from Figure 5 the tube 22a is rectangular in cross-section and of constant dimensions along its length while the tube 22b of Figure 6 is of variable cross~section along its length, being approximately square at its upper end and tapered in one dimension and flared in the other ; from that ~
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end to its lo~le~- end. The xectangular shape of the outlet end o4 the flight tube helps to ensure that markings applied by the apparatus do not have blurred edges.
~ In the arrangement shown in Figure 3 the flight tube 22 is of constant dimension along it5 length and no yreat difSiculty is encountered in obtaininy a true lamella flow of 2naterial from a noæzle end 25 thereof. However, with some lengths of tube conditions may arise in which , the gaseous jet and admixed particulate material o~cillate wl.hin the tube leading to accretion of the particulate material to the side walls of the flight tube 22.
In order to prevent the occurrence of unwanted oscillations and the consequent accretion of the particulate material to the side walls of the flight tube 22, baffle plate~
may be provided down the centre of the flight tube 22 to spli~ the tube in two length-wise. Indeed several bzffles may be provided splitting the flight tube along ~ts lenyth into several parts. Tests on such arrangements h~ve shown that the resultan markings are not impaired in an~ ~ay whlle accretion of material to side walls o~
th~ flight tubes 22 is p~ever.tedO
- It i-s also envisaged that use may be made of alternatiue methods of preventing unwanted oscillation of the mate~Lal - in the flight tube. ~Such a-lternative methods mav include~--~he use of annul~r i~let ducts for introducing hot g~ to ~e tlbe ~2-., .

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to augment ~e flow of the gaseous ~et therethrough.
~ccxetion is also prevented by lining the flight tube with a perforated lining plate, which also has the advantage of reducing the noise of the operation.
In the arrangem~nt shown in Figure 3 only one line 16 ' ~s shown connecting with the mixing ch~mber 18; however two o~ more such lines may be connected to the chamber 18l see Flgurc 4. In addition it ~s envisaged that, while the lines 16 are arranyed at an acute angle of 35 : to a longltudinal axis of the mixing chamber 18, in the embodiments illustrated, a~y convenient angle of entry m~y b~ used. In addition the entry ports need not be diametrically opposite one another, as shown in Figure 4, but mav be staggered along the length of the mixing chamber 18.

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The apparatus may also include purging means for purging the apparatus of particulate material at the end of work shift. This purging means may comprise a container ~0 for cleaning grit, sand, or the like material~ This ma erial may be fed into the feed device 14 via a venturi valve similar to valve 400 ~5 1 ~
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Thus, air rrom the compressor wiLl cause cleansing ~, material to ~e fed to the mixing chambers 18 as aforesaid, via the valve 40 and line 16 to purge the mixing chamber 18 and flight tube 22 of any residual particulate material.
The purging means may also comprise a fluiclised bed for agitating the sand in the container.
It is often desired to spray a material s~ch as small glass beads onto the road 24 to form a top re1ective layer of the marking 26, These beads are h~ld in a hopper 60, and may be agitated ~o form a fluidised bed. To feed these beads to the road they are passed down a tube 61 and through a pneumatically controlled venturi valve 63 onto the road 24.
The apparatus described above may be adapted for mounting on a vehicle 80, see Figure 1 and 2, which vehicle is of much simpler design than known road marking vehicles.
In the arrangement shown in Figures 1 and 2, there is a l~terally moving carriage 81. This carriage includes a feed means 14, and a hopper 60 to hold glass beads and the like. There are also two sets of flight-tube 22, mixing chamber 18, feed line 16, o~bustion chamber 48 and burner 20 one set at each end of unit 81 and thus one set on either side of the vehicle 80. In addition there are two tubes 61 running from hopper 60 r one tube disposed behind each flight-tube 22.

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As an alternative, there may only be one set of flight-tulbe, mixing chamber, feed line, ccmbustion chan~ber and burner, all of which may be mounted as a boom to swing to either side of the vehicle. This boom may be covered by a thermally insulating jacket to protect operative personnel from burns.
Although the apparatus described hitherto is provided with a fluidis~d bed feed means it may be useful in some applications to utili~e a gravity feed arrange-ment as shown in Figure 4. The particulate material r, can thus be fed to the line 16 via a line 84 and a venturi valve 85 of known configuration.
In a further modified apparatus (see Figure 7) a gas deflector 86 may be attached to the lower end portion 25 of the flight tube 22. This arrangement is utilisedto assist the adhesion and settiny of the sprayed on marking 26.
The apparatus described above has several major advant-ages in determining suitable marking materials which it may utilise.
In the conventional thermoplastic road marking materials, - the binder resins must melt to a state of high fluidity to enable the overall composition to be sprayed or flowed (screeded or extruded) onto the road surface. This limits the types of resin, or polymer, which can be used, .

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and also effectively lirnits the final performance of the road marking material. High fluidity results from relatively low molecular weiyht which in turn leads to low mechanical strength and touc~hness.
The materials capable of being used by the above apparatus do not have this limitation, in that it is apparently sufficient that individual binder particules should melt in order to adhereto the surrounding particles of filler, pigment, beads, etc. Thus binder polymers can be chosen of much higher molecular weight which give enhanced mechnical propert es over existing thermoplastic composit'ons.

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~ ' The individual components of the materials used do not need to be thoroughly compounded before application. Thus, a simple blend of polymer powder, pigment, aggregate and glass beads providing it is mixed uniformly before use, ~ apparently gives an homogeneous coating to substrates.

The apparatus is suitable no-t only for the use of thermo-plastic materials, but also for thermo-setting materials.
A typical thermo-setting type would be an epoxy powder coating material which comprises an intimate blend of an epoxy compound and a reactant, which do not effectively 2~

react to give a polymer until a threshold tempera-ture above 100 is reached. If used in the above apparatus, such particles would melt to fuse into a coherent whole and a chemical reaction would occur to improve the mechanical properties still further.
A composition, particularly suitable for use in the apparatus described above to provide markings on highways ; or airport runways, etc., is one such as described in ~ our ~atent Speci~ica~ion WoO1344255 e ~titled "Improvements Relating to ~oad marking."
Although -uch a material is described as particulate~
material in other forms may also be used in the apparatus e.g. particulate materials in a liquid suspension are envisaged.
lS The vehicle 80, may incorporate any convenient sighting or sensing device for alignment of the flight tube 22 of the spraying apparatus over the portion of the highway 24 to be marked.
The vehicle 80 is driven along the highway 24 and a marking 2~ applied thereto. The thickness of the marking may be in the range 0.3 - 4.0 n~and is prefPrably in the range 0.5 - l.S mm.
The operation of the apparatus may be automatic in response of sensing of areas to be marked or the apparatus may be 3~

controlled manually from the console 42 by the vehicle driver. In either case the on-off cycle may be achieved ~! by opening and closing the venturi valve 40 of the feed device 1~ to interrupt the feed of the particulate material.
In shoxt line markings interruption of the burner operation is not necessar~; however, in long line markings where long gaps are formed between the markings it is economical to shut off the burner 20.
The end of line definition is remarkably clear and no ghosting in the gaps between markings is evident.
The high impact velocity of the marking material on the road surface improves i-ts adhesion.
In addition almost perfect resolution and material ~5---distribution is~ achieved with the spraying apparatus.
In use, the burner 20 creates a hot gaseous jet in a reducing atnos~ere capable of raising the ternperature of the particulate material without charriny to above its melt temperature which, according to the heat softenable portion of the particulate material used, will be 100 to 430 C. The heat generated by the burner 20 must therefore be in the order of 1 M BT~s per hour in order to provide sufficient latent heat in the hot gaseous jet to enaDle it to affect the particulate materials as aforesaid.
Other advantages of usiny the apparatus described above to carry out the met}lod of spraying particulate material 3~7 ,,~

are:
(i) low cost compared with presently available line spraying equipment;
(ii) operation as a continuous process by one man using a single vehicle;
(iii) short warm up periods for operation conditions to be reached;
(iv) low pigment level requirement;
~v) instantaneous colour change where hoppers 44 and venturî valvec are utilised;
(vi) lower fuel consumption compared with known arrangements;
(vii) less environmental pollution;
-(viii) less hazard to operatives- from easily shielded applicator assembly;
(ix) no hot materials to handle or maintain in liquified condition;
(x) temperature sensitive materials may be used because o~ short duration at high temperature.
20 In the arrangement described a flashback burner is used to create the gaseous jet. In alternative arrangements a gas turbine or free piston gas generator may be used.

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Further modifications may also be made to the apparatus ~'15! with the scope of the invention. For example, a variable geometry flight tube as shown in Figure 9 might be employed rather than the fixed flight tubes described above in order 5 to adjust the width of markings and form symbols such as arrows. Furthermore, the ingredients of the marking material need not all be injected into the flight tube at the same point and the aggregate, for example, could be injected upstream of the burner.

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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for applying to a road surface, marking material which is fusible onto the surface, the apparatus comprising means to burn a gaseous fuel in air under pressure to provide a supply of heated pressurized gas, duct means to direct the hot gas onto the road surface to be marked and means to inject a supply of marking material in unfused form into the hot gas stream within the duct means downstream of the burner means, thereby to cause the marking material to impinge on the surface, characterized in that the duct means comprises a first elongate mixing chamber portion down which the hot gas is directed and into which the marking material is injected and a second elongate outlet duct portion co-axial with and downstream of the first portion, the outlet duct portion being of rectangular cross-section and having a ratio of length to maximum cross-sectional dimension of at least 4.75:1 so that the distance of the point of injection of the marking material from the road surface to be marked is such that at least some of the marking material is fused before the marking material impinges on the surface.

2. Apparatus as claimed in claim 1, characterized in that the ratio of the length of the outlet duct portion to its maximum cross-sectional dimension is between 4.75:1 and 9:1.

3. Apparatus as claimed in claim 1, characterized, in that the ratio of the length of the outlet duct portion to the maximum cross-sectional dimension is approximately 6.5:1.

4. Apparatus as claimed in claim 1, 2 or 3, in which the outlet duct includes a baffle extending longitudinally of the duct.

5. Apparatus as claimed in claim 1, in which the injection means for the marking material comprises a container for the material, at least one supply line connecting the container to the mixing chamber portion and means for supplying compressed gas to the container to entrain the material and carry it through the supply line.

6. Apparatus as claimed in claim 5 in which the container is a fluidized bed and includes at least one Venturi valve for controlling the flow of material from the container.

7. Apparatus as claimed in claim 6 further comprising a hopper for the marking material, a conveyor for transferring material from the hopper to the container and a float valve for determining the level of material in the container and controlling the conveyor in response thereto.

8. Apparatus as claimed in claims 5,6 or 7 and further comprising means for supplying purging material under pressure to the supply line to clear the supply line and duct.

9. An apparatus as claimed in claims 1, 2 or 3, in which the gaseous fuel is ignited in a flashback burner and burns as it is passed through a combustion chamber, producing a resultant stream of hot gas.

10. An apparatus as claimed in claims 1, 2 or 3, in which the gaseous fuel is liquified petroleum gas.

11. A road marking vehicle comprising a self-propelled chassis and an apparatus as claimed in claim 1, having two ducts, and associated with each duct a burner and a supply line, both supply lines feeding from a common container and in which the supply lines, burners and ducts are rigidly mounted on the container such that one duct faces the road surface on each side of the con-tainer.

12. A road marking vehicle as claimed in claim 11, in which the container is traversibly mounted on the vehicle.