Making Milk Cans

Sun (Auckland), Volume IV, Issue 992, 7 June 1930, Page 6

Making Milk Cans

This is the eighteenth of a series of informative articles that are being published in THE SUN weekly throughout 1930, describing many of New Zealand's most important industries.

INTERESTING PROCESSES IN AUCKLAND FACTORY WE live now in an age of specialities, Alex. Harvey and Sons have specialised in the manufacture of milk and cream cans for 43 years. The dairy farmer specialises in the production of milk. To obtain his production at a minimum cost he must support those who specialise in the subsidiary industries to the dairy industry. A description of the manufacture of milk cans should therefore prove of interest not only to the dairy farmer, but to all who are interested in New Zealand’s future.

The manufacture of the Harvey Seamless Milk and Cream Cans is performed throughout only by skilled tradesmen who are required to serve an apprenticeship of five years before being put on to this work. The utmost care is used from the first to the last operation to ensure that all cans are up to the extremely high standard set by their policy of quality first.

On several occasions experts from the leading steel mills of England have visited Harvey’s works and studied the manufacture of the cans right through all the different stages under actual -working conditions, with

the view of providing steel that is the best suited for this particular purpose. The result is that the steel used in tha manufacture of Harvey Cans is the most perfect material for the job that it is possible to obtain anywhere in the world. CUTTING STEEL SHEETS The first stage Is the cutting out of the flat sheets to the correct size. This is done in a. guillotine-shearing machine which will cut heavy gauge steel like a knife cutting butter. After cutting, the raw edges of the sheet are pickled in acid to ensure absolute freedom from scale. The flat sheet is then rolled into th£ form of a

cylinder in a rolling machine. The next operation is performed by an electric spot-welding machine which tacks the edges of the cylinder together The spot-welder just fuses the metal together in several tiny spots along the seam so that the material is held in the correct position for the welding of the side seam. Great care must be exercised to obtain just the right amount of over lap. This over-lap must be just equal to the thickness of the metal to obtain a perfect weld. The cylinder is now passed on to the electric seam-welding machine, which automatically welds with a seamless effect. Where the metal has been welded is then hammered

under a power hammer to restore it to its natural hardness. We now have a cylinder without even the sign of a seam, the metal being of uniformity right roupd the cylinder. The cylinder is now taken to the spinning lathes, where the shoulders and neck are spun into shape. SPINNING It might be mentioned that, of all metal working, spinning is considered the hardest branch to learn. It takes a man many years to acquire the art of spinning metal correctly. Th-j spinning requires very careful manipulation of the metal to keep it to au

even thickness, and also in order not to over-strain the metal. The spinning is done in two operations. The first lathe brings the neck of the can down to nearly the correct size, and then it is passed on to another lathe, where the neck is sized accurately so that the one lid will fit any can. On this same lathe the top is trimmed off, and ft flftetftt toA which has been previoaftly rolled Into a circle of the correct diameter is placed into the top of the neck, and the metal rolled over It so that the rod is completely covered. This gives strength and rigidity to the neck of the can. FIXING THE BOTTOMS The bottom of the can is stamped out of a flat sheet In a drawing press, and then trimmed to the correct size in a trimming lathe. The bottom of the can is then tacked on with an electric spot-welding, which merely tacks the bottom on to the body of the can in several tiny spots in order to hold it in position for the complete welding. It is now passed on and welded all round in a special bot-tom-seam welding machine. Oxy-acetylene welding is also used to a certain extent for welding on the bottoms, but It Is gradually being replaced by the automatic electric welding, which is both faster and more uniform. The body of the can is now ready to be taken to the tinning shop. TINNING THE CANS The first operation in the tinning shop is to wash the cans in an alkaline solution to get them perfectly clean and free from grease and oil. They are then pickled in a bath which consists of a weak solution of sulphuric

acid and water, heated by steam to approximately ISO degrees. The cans are kept moving in this pickle until every vestige of scale is removed.

They are then taken out of the pickling solution and swilled in clean water, and scoured all over with fine sand and water. Any little black specks showing must be completely removed either by scouring with fine sand or by scraping with a sheet scraper. When perfectly clean the cans are ready for the tinners. The tinner first places the can in the flux pot. which consists principally Gf hot palm oil. After being thoroughly soaked in this flux the can

is lifted out and immersed in rough tinning pot. This pot contains pure molten tin, with its surface covered with palm oil to a depth of about four inches. In the bottom of this pot. running in the molten tin, are power-driven rollers which cause the can to revolve round and round in the tin. The tinner brushes the can with palm oil as it revolves and exposes part of its surface above the molten tin. When thoroughly tinned the cans are lifted out with special tongs and brushed inside and out with flux. They are then placed in the second tinning pot, which is similar to the first. After being coated with tin in this pot the can is carefully inspected, and if an * little black specks should show —even one the size of a pin-point —the can has to' be re-scoured, and all the tinning done over again. THE TWO BRANDS The Seamless Bottle-neck Cans (“R.V." Bfand> are made out of the very best quality black steel sheets, especially manufactured in England for this particular purpose. These are grease-tinned, having in all four coatings of tin, being dipped first i® one pot and then in another until they have been dipped four times. The telescope, or straight-sidea cans (“Ideal” Brand), are manufactured from the very best tinned sheet* procurable, and are of the best charcoal crocodile finish. The term “crocodile” finish is used because the sheets have a heavy coating of tin whi® gives it the same lined appearance crocodile leather. , If the little points of care are noteo. the above cans have an exceptional long life; but in the majority of c * a * f the cans receive nothing but abuse that it is possible to give the That Harvey’s cans remain in after many years of buffeting in t dairy factory and on the farm ve •- definite proof that they are made the right materials manufactured 1 | the right way.