products according to prior art used as dry spray for the manufacture of cast iron pipes by centrifugal casting have some disadvantages . the inert mineral filler added to the mix contributes to increasing the risks of making moulds dirty and the formation of inert mineral inclusions in the cast iron that can appear as surface defects on the pipes . furthermore , the applicant has observed that although the addition of a strongly reducing agent such as aluminium protects the shells and their life , in some cases , it can increase the risk of occurrence of unacceptable pitting defects on the surface of the pipes . therefore , the applicant &# 39 ; s objective was to develop products that protect the user from these disadvantages . these products comprise an inoculating alloy , for example based on ferro - silicon , or a mix of inoculating alloys , possibly a mineral filler and a reducing agent with a content of between 0 . 3 and 18 %, composed of a metal that is volatile at the temperature of the liquid cast iron , that may be a metal from column 2 in the mendeleiev classification , and preferably a metal from column 2a in the periodic table of the elements . the preferred metals are calcium or magnesium or alloys containing at least one of these metals . silicon alloys are particularly suitable , particularly the casi alloys . thus , the following alloy compositions can be used ( by weight ): either between 0 . 3 and 4 % by weight of magnesium , and preferably between 0 . 5 and 2 %. it is found that the casting mould starts to get dirty in the form of whitish traces of mgo if the content is higher than 4 %. or 15 to 40 % by weight of casi alloy , representing a calcium content of between 4 and 14 %. tests carried out by the applicant have shown that ferrous alloys of the fesica type , typically containing more than 10 % iron and frequently called “ casifer ” containing ( by weight ): si 47 - 53 %; fe 35 - 48 %; mg 2 - 12 %; al 0 . 2 - 1 . 5 %; ca 0 . 1 - 1 . 5 %, rare earths 0 - 2 %, give disappointing results , well below the results obtained with mixes according to the invention . the corresponding quantities of the different constituents in the final mix were evaluated as a function of the defects that can arise as a result of overdoses . furthermore , for safety reasons related to preparation of the products , the reducing metals or reducing alloys are not used alone , but rather in the form of a premix with an inert substance , preferably calcium fluoride , magnesium fluoride or a mix of these two fluorides . for maximum efficiency , the strongly reducing metal alloy content in the premix is preferably between 15 and 60 %. the size grading of the products is less than 400 μm , and is preferably less than 250 μm . fine particles smaller than 40 μm and preferably smaller than 50 μm are excluded to prevent dust emission during use . a mix was prepared according to prior art with the following constituents : 85 % ferro - silicon with 75 . 2 % of si , 1 . 3 % of ca and 0 . 45 % of al , with size grading of between 50 and 200 μm and 15 % of fluorspar with a size grading of between 10 and 150 μm . this product gave satisfactory results when used as a dry spray as a reference test ; the pipes were stripped after 55 seconds of cooling and the thickness of ferritic cast iron measured on pipes made in this way was 35 microns . however , the shells were slightly attacked . a mix according to the invention was prepared from the following constituents : 55 % ferro - silicon with 75 . 2 % of si , 1 . 3 % of ca and 0 . 45 % of al with size grading between 50 and 200 μm and 45 % of a mix composed of ⅓ fluorspar between 10 and 150 μm , and ⅔ of calcium silicide with 60 . 1 % of si , 31 . 7 % of ca and 4 . 3 % of fe . when used as a dry spray this product gave satisfactory results ; the pipes were stripped after 45 seconds cooling and a thickness of 25 μm of ferritic cast iron was measured on the pipes made in this way . however , there was no visible attack of the shells . therefore , this type of product gives better results than the product mentioned in example no . 1 . a mix of 50 % of magnesium powder with size grading between 50 and 250 μm , 25 % of magnesium fluoride with size grading between 40 and 250 μm , and 25 % fluorspar with size grading between 40 and 250 μm , was prepared . a mix according to the invention was then prepared consisting of 3 % of the previous mix and 97 % of ferro - silicon with 75 . 2 % of si , 1 . 3 % of ca and 0 . 45 % of al with a size grading between 50 and 200 μm . when used as dry spray test , this product gave results considered to be better than those obtained in examples no . 1 and no . 2 ; the pipes were stripped after 37 seconds cooling and the pipes thus made were found to have a ferritic cast iron thickness of 30 μm . the surface condition of the parts was considered to be excellent . a mix according to prior art was prepared with an equivalent composition of the mix in example 3 , composed ( by weight ) as follows : 43 % of ferro - silicon with 75 . 2 % of si , 1 . 3 % of ca and 0 . 45 % of al with size grading between 50 and 200 μm and originating from the same batch as the ferro - silicon used in the previous example . 29 . 5 % of a fesimg type alloy with size grading between 50 and 200 μm , analysed to contain 50 . 7 % of si , 42 . 0 % of iron , 5 . 2 % of mg , 1 . 2 % of ca and 0 . 35 % of al , 26 % of metallurgical silicon powder with size grading between 50 and 200 μm containing 98 . 6 % of si . 0 . 75 % of magnesium fluoride with size grading between 40 and 250 μm , 0 . 75 % of fluorspar with size grading between 40 and 250 μm . when used as a dry spray , this product gave results significantly worse than those obtained in example 3 . pipes were stripped after 50 seconds cooling , the observed thickness of ferritic cast iron on the pipes thus made was 35 μm , and absolutely unacceptable pitting was observed on the surface of the parts with a density of the order of 25 per m 2 .