48 



Hardwood Record — Veneer 6c l^inel Section 



June lU, 1921 



The Madison Laboratory on Casein Glues 



i cinifniiK ii uoiii ii'Hi' ;;> I 



to fresh quick lime to cause it to sUike to a powder. It should or iduniinum, as the alkali usually present in casein j,'lucs will 



then be made fine enouph to pass entirely through a 60-mesh attack these metals. No provision need be made for heating as 



sieve. Commercial powdered hydrated limes are also suitable. casein glues must not be heated. A type of mixer that has proved 



Silicate of Soda. — The silicate of soda is in liquid form and cor- satisfactory at the Foreft Products Laboratory is a power cake 



responds to the grade which appears on the market for preserv- dough mixer used by bakers. The machine has a double acting 



in^ eggs or for adhesive purposes. The various samples which paddle and may be operated at three different speeds. Some glue 



have given satisfactory results at this Laboratory have had analyses manufacturers have devised inexpensive machines which do good 



included within the following ranges: work and which embody the essential points of thorough agitation 



a -r 1 iQ 1 I /IT and ease of cleaning the mixing bowl. 



Specific gravity I . )t5 to 1 .4Z 



Density (Baume scale) 40.31 to 42.96= Application of Glue 



Sodium oxide 9.38' < to 9.88' v ,--1 1 11 



_,,. 1 t A t I 2T lot- Casein glue may be applied to the wood either by hand or a 



Silica 3 1.41 ' to iZ.iO r , 1 1 ■ 1 I , . , , 1 



machine spreader. In applying by hand, a wire brush or a metal 



This formula as stated gives a glue of considerable water re- . j u i£ j ■ j ^u 1 i_ j 



, scraper gives good results. It desired the glue may be prepared 



distance. It has formed the basis for a large part of the later ex- [ ■ . » _ j • 1 ■ ■ ^ -^l i_ • ii 



** "^ of proper consistency to spread on irregular joints with a bristle 



perimental work on casein glues at the Forest Products Labora- . l -ri. j- * j 11 » r l- j • 



■^ ^ brush. I he ordinary corrurated roll type of machine spreader gives 



torv. Modifying the proportions of materials and the addition , 1. tr u 1 u u u j * l ti_ 



^ J & f f good results. Lnough glue should be spread to cover both sur- 



of still other components give glues of very desirable qualities. , c .u • » j 11 . u u . c 



K B B .7-1 faces ot the joint and a small amount should rquceze out from 



The degree of water-resistance and the workable life of the glue .1 • • . u ■ I- J 



^ ^ the joints when pressure is applied, 



after mixing can be greatly varied. This property of the wet mi.x -p, t ■ \-c c ■ 1 • -j li r 



•^ & .» I- r- .- ^ I ^^2 working lire or casein glues varies considerably rrom a 



glues, namely the variation of the components to attain glues of , 1 \ 1 c j > ■ . u u » J 



^ -^ ^ few to many hours. .-A glue ot moderate consistency should stand 



desired qualities is one of the chief advantages over the dry mix . 1 . t r c L J 1 u J u- L 11 



^ at least for tour or hve hours, and glues may be made which v^rill 



type. The dry mix glues on the other hand require less technical 1 . r 1 TL c» ( It u ij u • J J 



J t' J b -I l^gj ^^j. many hours. 1 he htness or a glue tor use should be judged 



knowledge on the part of the user than do the wet mix type. , . ■ ^ j i- -i 1 -^ 1 -r i 



^ by Its consistency, and, ordinarily, as long as it can be unitormly 



Prepared Casein Glues spread, a good glue will give good results. The time that may 

 Commercial casein water-resistant glues are of the dry mix elapse betw^een the spreading of the glue to the wood and the press- 

 type of which there are at present four on the market. They ing will depend upon several factors, chief of which are: ( I ) mois- 

 are made by secret formulas and the details of their method of ture content of wood, (2) consistency of glue, (3) kind of wood, 

 manufacture are not public. Directions for mixing these glues (4) quantity of glue applied, and (5) temperature of the wood 

 are furnished by the manufacturers and should generally be fol- and glue. The time should be correspondingly reduced if the 

 lowed by the user. The principal points to be observed in the wood is of an open porous nature and of a low moisture content, 

 mixing of prepared casein glues are: or if a thin spread or a thick, heavy glue is used. A high tem- 



1. A thorough mixing of the dry glue from each or all contain- perature causes the moisture to disappear more rapidly from 

 ers before adding to the water. This is advisable due to segrega- the glue layer and also hastens the setting of the glue. In general 

 tion of ingredients of different specific gravities which may occur the pressure should be applied while the glue is yet in a wet 

 during shipment from the factory to the consuming plant. Sift- condition in order to obtain contact between the uncoated wood 

 ing is not advisable, as it may remove from the glue some essen- and the glue layer. If the glue becomes too thick, poor contact 

 tial component. will result. In most cases, if pressure is applied within ten to 



2. Proportions of glue and water should always be weighed, fifteen minutes good results will be obtained. Under other condi- 

 and not measured. tion a longer time may elapse. 



3. The glue should be added slowly to the water, accompanied 

 by vigorous agitation in order to avoid a lumpy mixture. 



4. After the glue is well mixed into the water the stirr ng should Sufficient pressure should be applied to bring the layers of wood 

 continue more slowly until all particles are thoroughly dissolved in'o close contact with the glue. A pressure of 100 to 150 

 and the glue appears of a smooth, creamy consistency. pounds per square inch is usually considered ample. This will 



5. The desired consistency of the glue should be attained dur- necessarily vary with the consistency of the glue and the charac- 

 ing the mixing and no attempt should be made to thin the glue ter of material being joined. Greater pressures are necessary 

 should it become too thick in use. It should be mixed only as fo"" irregular surfaced material and thick glue mixtures than with 

 fast as it can be used in the proper condition. ^^'^ opposite conditions. The time under pressure may vary from 



The proportions of dry glue and water should in general be a ^>alf liour to a much longer period. Good joints' have been 



used as directed by the manufacturer. However, the exact pro- obtained by pressing for only one-half hour. .A longer period will 



portions will vary with (1) different glues, (2) different shipments probably give better and more uniform results. Where it is con- 



of the same glue and (3) the kind of work for which the glue venient retaining in clamps over night is advisable. 



is to be used. Only average proportions can be stipulated by .After the material is removed from the press, it should preferably 



the manufacturer, and the operator, in order to obtain satisfac- ''^ allowed to condition before being finished. The time required 



tory consistencies, may find it necessary at times to vary from for conditioning will depend upon the size of the stock, the 



the average proportions specified. moisture content of material before gluing, the condition under 



_ which it is seasoned and the requirements of the finished product, 



lype of Mixer at r ■ 1 1 • 1 . 1 • 



-J,. ,. . . . 1 , , 1 '^ uniform moisture content of approximately what is desired in 



1 he ordinary type ot mixers used tor animal and vegetable .1 c 1 . 111 .■ 1 ■ 1 1 r 



, 11 I 1 f 1 -T-1 *"^ nnal piece should prevail in the material betore it is put 



glues are not well adapted tor casein glues. The prime requisites ., , , , . , . 



r ■ r \ 1 , , - .... , rii through the hnishmg process. 

 tor a mixer tor these glues are ( I ) rapid agitation and preferably 



different speeds of the paddle, (2) a glue pot that can be readily Storage of Casein Glues 



cleaned preferably one that can be detached from the machine Dry casein and casein glues will keep for a long time if stored 



itself and (3) a glue pot of metal that will not corrode under the under proper conditions. When bought in large quantities they 



action of alkali. The mixing pot should not be of brass, copper, (('(iiitinticd on pinji om 



